Overview of the Study

The study conducted by Sui et al (2015) analyses the association between development of depressive symptoms with that of television watching and car riding behaviors. The observational longitudinal study conducted on participants analyzed sedentary behaviors as a potential factor for the development of depressive symptoms. Depicting of sedentary behavior in the last 10 years has been seen associated with an integrated risk factor for negative health impact that can be distinguished from physical activity. Related experimental and observational studies in the domain depict direct association between poor physical health outcomes such as mortality, risks of cardiovascular disease (CVD), hypertension, diabetes, cancer and metabolic health disorders with that of sedentary behavior (Chastin et al, 2015). The paper includes the World Health Organization recommendations in regards to limiting of sedentary time amongst adults and youths.

The unclear association between mental health outcomes and sustained sedentary behavior leads to the association of four longitudinal investigations that can associate depressive disorders with that of sedentary behaviors. The consideration in the paper to include TV watching and car riding is supported from recent studies in the domain (O’donoghue et al., 2016). One of which has depicted depressive outcome with that of TV watching and sitting in car is an important parameter in sedentary behavior. The National Household Travel Survey 2009 data provides that an average American spending almost an hour per day in order to travel by car, excluding road trips. There are a considerably less number of studies that analyze the influence of PA on depression risk and sedentary behaviors. A more detailed analysis of the interaction of PA with sedentary behavior and risks of depressive symptoms is needed.

The importance of this paper is in the fact that there is an increasing burden of depressive disorders worldwide. In order to resolve this public health issue, it becomes important that the modifiable factors or characteristics are recognized which can prevent depression (Bailin, Milanaik & Adesman, 2014). The study has specifically aimed to diagnose two integral sedentary behaviors that might lead to depression along with the associated risks of developing depressive symptoms. The study also aims at analyzing if PA modified the effect of sedentary behaviors and depression symptoms. The study over a 20-year follow-up conducted amongst a group of women and men who were enrolled at the Aerobics Center Longitudinal Study (ACLS).                

Study design, methods, and statistical analysis

The study is ACLS (Aerobics Center Longitudinal Study) conducted on women and men coming from 50 states, who have been examined at the Cooper Clinic in Dallas, TX. The patients were either self-referred or referred by employees or physicians, who had come for their periodical preventive check-up and counseling for lifestyle and health-related behavioral factors. These patients were briefed by the ACLS and they provided their consent for a follow-up study.

Study design, methods, and statistical analysis

The cohort study included data from the 1982 survey as the baseline measure, where information regarding sedentary behavior was collected. From a total of 11,972 participants, 1,830 were excluded as they did not meet the criteria for selection and had depicted myocardial infarctions or stroke or coronary bypass operation or depression. The eligible participants of 4,802 completed the 10-item Center for Epidemiological Studies Depression Scale (CES-D 10) in the period 1990 to 2005.

In order to record depressive symptoms between 1990 to 2005, the CES-D 10 was assessed and participants were made to respond to 10 items on a 4-point ordinal scale. In the ordinal scale, eight of the ten CES-D items assessed varied factors of depressive mood and the other two undertook reverse record items such as happy mood, hopeful state. A measure of greater than or equal to 8 on the CES-D depicted the presence of elevated depressive symptoms.

The baseline measures included demographic, health-related and socioeconomic status. The measure of PA was undertaken by means of questions asked to participants to report the total time that is spent in doing vigorous and moderate PA (MVPA) in the last 7 days. In order to not meet PA recommendations in the current study, it was total time greater than or equal to 2.5 hours and those who had performed lesser than 2.5 hours of MVPA. There were other covariates that were included in the study such as smoking, heavy drinkers, BMI, cardiorespiratory fitness (CRF) was assessed during the study.

The study was conducted using statistical software SAS, version 9.3 by setting alpha set at P<0.05. The baseline nature of the study population was characterized by depressive symptoms and differences in covariates were analyzed using –test and chi-square test. In order to analyze the association between the risk of developing depressive symptoms and sedentary behaviors, logistic regression models were applied. In order to denote strength in the association, Odds Ratios (ORs) and 95% confidence intervals (CIs) was reported to be an index. There were three models that were tested, age and sex-adjusted model, multivariate plus MVPA model (in hours/week) and multivariate-adjusted model with covariates of gender, age (in years), marital status (currently married or not), high school or less education (by yes/ no), current smokers (by yes/ no), employment status (currently working or not), BMI (in kg/m2) and diabetes (by yes/no). An initially linear trend of the risk of depressive symptoms with that of sedentary behavior was analyzed and then stratified analyses across MVPA groups was conducted. The second analyses were conducted to understand the MVPA association with depressive symptoms or sedentary behaviors. The final analyses were conducted by adjusting for CRF data (n=4709) as it was an objective indicator for habitual PA.                      

Results

The study results were analyzed after 9.3 years with 564/4802 participants (12%) had developed depressive symptoms. The results revealed that the participants who had developed depressive symptoms were younger, not married, and female and had longer time spent watching TV or riding a car and combined sedentary behaviors. Participants were at 27% greater risk of developing depressive symptoms, which rode greater than or equal to 9 hours/week as against those participants whose riding time was lesser than 5 hours/week. The results were derived post accommodating for gender, age, marital status, education, employment status, BMI, current smoker and diabetes (P trend =.03). Adjusting for MVPA did not materially change any observed associations. Individuals were 42% at higher risks of developing depressive symptoms who watched TV greater than 10 hours/week as compared to individuals who watched less than 5hours/week after taking into consideration multivariate adjustment (P trend =.003). Adjusting for MVPA revealed individuals who watched between 5 to 10 hours/ week TV were at a 35% higher risk of developing depressive symptoms. Such risk factors were 52% higher for individuals who watched more than 10 hours/week TV. Combined sedentary behaviors of watching TV and car riding revealed participants, who reported 12 to 18.9 hours/week and greater than or equal to 19 hours/week of sedentary behavior were at 35% and 74% greater risks from development of depressive symptoms as against those who reported less than 12 hours/ week, post adjusting MVPA (P trend <.001).

The study conducted analysis between depressive symptoms and sedentary behavior variable with multivariate-adjusted OR and 95% CI with each 1-hour increment was 1.017 for TV viewing, 1.024 for car riding and 1.018 for the combined behaviors. Adjusting for MVPA did not impact the association and it was found that OR and 95% CI for each 1-hour increment was 1.016 for TV viewing, 1.023 for car riding and 1.017 for combined behaviors.

Examining the impact of MVPA in modifying the association between depressive symptoms and sedentary behaviors, multivariate-adjusted analyses revealed a positive association between times spent in watching TV, riding a car and risk of developing depressive symptoms in participants who did not meet the PA recommendations. There was a linear positive association between long hours of combined behaviors and a higher risk of developing depressive symptoms amongst individuals who met and did not meet current PA recommendations. Analyzing across three groups of MVPA revealed patterns with similar nature of positive association in time spent in combined sedentary behaviors and depressive symptoms in each MVPA categories.           

 The study’s primary analyses were aimed at finding a relationship between time spent in car riding, watching TV and combined behaviors association with depressive symptoms. The analyses of the study revealed over a 9.3 years period study that longer the time spent in TV watching or in car riding or in combined behaviors greater is the risk factor for developing depressive symptoms. Lesser time spent on watching TV or in car riding or combined behaviors was found to lead to lesser risk factors for the development of depressive symptoms (Catrett & Gaultney, 2009). MVPA played a significant role in buffering between the two sedentary behaviors and combined sedentary behaviors. Individuals who met the current PA recommendations, there was no significant association that was observed between watching TV and car riding.  However, for individuals that did not meet the current recommendations for PA, there was an indication between the development of depressive symptoms with that of car riding or TV watching. In case of prolonged combined presence of sedentary behaviors, there were no significant alterations that MVPA was seen to be reducing on depressive symptoms. In spite of MVPA levels, individuals who spend more than 19 hours/ week in combined sedentary behaviors, there were significantly higher risks of developing depressive symptoms (Owens & Adolescent Sleep Working Group, 2014). A major indication of the finding is that this study was the first longitudinal one which depicts direct relation between the two popular sedentary behaviors with risks of developing depressive symptoms.  

The role of PA was found associated in reducing the risks of non-clinical depressive symptoms along with clinical depression amongst adults. There was found to be a significant association between PA and formal exercise training with depressive–related mortality amongst patient with heart failure and heart disease (Rhodes, Mark & Temmel, 2012). PA association with sedentary behavior and depressive moods is controversial as in certain studies there have been seen no significant impacts and in order, there have been seen to be considerable impacts. In the current study, the higher risks of depressive moods were found to be associated with TV viewing and car riding and did not meet the recommendations for PA. At the time of combined sedentary behavior analyses, there was found to be a positive linear trend throughout tertiles regardless of MPVPA levels. This is the unique finding from this study which indicates the deleterious effects where very high levels of sedentary behaviors might not be easily be offset even in presence of PA guidelines. In the upper range of current guidelines greater than equal to 5 hours/day results were found to be consistent with PA, which attenuates sitting or depression relation. With the new dimension of sitting in the car being added in the study, which was included only in few other studies reveal significant applicability of the study. The paper’s integral finding is that adding each hour spent in the car has been found to be associated with almost 2% higher risks from depressive symptoms. In this case, the participants sat in the car for more than or equal to 9 hours per week and posted 28% higher risk in developing depressive symptoms as when compared to individuals who spent less than 5 hours per week sitting in the car.      

It is crucial for a study to check for its internal validity to establish evidence supporting the claim regarding cause and effect. The analysis of alternative explanations to the findings is undertaken here. The scope of the present work is able to confirm previous work and also provide an expansion to existing literature by depicting the adverse association of car riding with depressive symptoms. There are certain inconsistent findings arising from the study design and other factors in cross-sectional studies.   

There has been less number of studies conducted on sedentary behavior and health outcomes. Till date, the role of sedentary behaviors in developing depressive mood has been undertaken in 10 studies which include 6 cross-sectional and 4 longitudinal reports. Across all cross-sectional studies, there was found a positive association between excessive sitting times, which is mostly screen-based behaviors regarded as total sedentary behaviors with depressive moods. 2 cross-sectional studies did not establish any significant association between depressive moods and TV viewing. An important finding from Dittmar and colleagues depicted the direct association of TV viewing with depressive symptoms. This study by Dittmar is critical is supporting the internal validity of the study. This study is able to provide partial validity for the current study. In another study by Zhai, Zhang & Zhang (2015) sedentary behavior which included TV viewing and prolonged use of internet use was found associated with pooled RRs (Relative Risks) of depression. This study undertook quantitative summaries of evidence from observational studies in a meta-analysis. The study collected data from PubMed and Web of Knowledge, Chinese National Knowledge Infrastructure and Wanfang databases. Data were collected up to 15 January 2014 for summary risks (RRs) estimated by random effects model. The meta-analysis included 110 152 participants and 11 longitudinal studies with 83014 participants.        

PA level of association with depression and sedentary behavior was found in the SUN Cohort Study, where a reduced sedentary index was depicted to be an integral factor for reduced risks from a mental disorder with low PA levels (Stierlin et al., 2015). The outcome was, however, could not be established during PA high levels.

Another study from the Australian Longitudinal Study on Women’s Health (ALSWH) depicted that women who sat more than 7hours/ day in front of the TV and did not do any PA experienced three-times higher rates of likelihood from depressive symptoms compared to those women who sat less than or equal to 4 hours/ day and included PA guidelines.   

The causality inference depicts a drawing of conclusion regarding the causal connection between conditions of the occurrence of the effect. In the current analyses response to the effect variable when the cause is altered is analyzed. There are various studies that support the findings of the current study with slight alterations in the cause of the study.  

Findings from Nurses’ Health Study by Lucas and colleagues reveal that TV viewing and screen time is positively related with incident depression in women who spent more than 21 hours weekly in watching TV compared to those who viewed less than 2 hours. This study supports the current study’s findings to establish its internal validity. The findings from Lucas and colleagues and other longitudinal studies have given evidence regarding the association of sedentary behaviors with the risk of developing depression. The study supports findings from the Sui et al (2015) paper as TV viewing has been found here to be positively associated with incident depression. This study also establishes the causality of inference.

In another study of English Longitudinal Study of Ageing (ELSA) was consistent with the paper of Sui et al, (2015). In the paper by ELSA, longer time spent in watching TV greater than or equal to 6 hours/day was found to associate with higher depressive symptoms as compared to individuals who watched TV less than 6 hours/ day. This study also establishes the causality of inference where the cause was a bit changed to more than or equal to 6 hours/ day from the current study’s 10 hours/ week. 

The above appraisal of the study reveals its uniqueness and very few studies have been conducted in the domain that aims at establishing a relationship between depressive symptoms with that of car riding behaviors as sitting in the car is a new factor recognized in the study, which might increase depression risk factors. The mechanism which can explain sedentary behavior with that of risks of depression has not yet been fully understood. There have been several hypotheses, which have been proposed which include social isolation, withdrawal or displacement. Most studies have reported a positive association of TV watching with depression, supporting the current study’s findings. Biological or psychological factor recognition might be able to establish a link of sedentary behaviors with that of depression (Tremblay, Colley, Saunders, Healy & Owen, 2010). The beneficial outcomes from PA on depression could be further strengthened from biological changes in experimental studies. The external validity of the study can be stressed on its capability to draw findings from a large well-established cohort comprising of adult men and women population with 20 years follow up. Though the study has been longitudinal in nature and conducted statistical analyses for establishing its results, there need to be further studies that reject or conform to the study’s findings.    

Conclusion

The study’s findings have been found to be consistent and extend beyond previous research work that has been conducted in the current domain. Earlier studies have indicated that sedentary behaviors might be the risk factors for depressive symptoms. There are certain limitations to the study such as taking into consideration ACLS population as a representative of the US population, sedentary behaviors and MVPA being self-assessed, observed effect of modification from MVPA interpretation needs to be accomplished in a more careful manner, assess changes in sitting time that took place during long follow- up and ignoring the episodic nature of depressive disorders. Future studies in the domain need to overcome these limitations while developing their study. Sedentary behavior and MVPA have been found to be positively associated with depressive symptoms. The scope of the current study requires interventions which can reduce two sedentary behaviors and allow increasing of MVPA for enhancing overall health outcomes amongst the adult population.

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